The Republican presidential nominee has had sharp criticism for Obama's approach — but has said little about what he would do differently.

Mitt Romney's foreign policy argument against a second term for President Obama has been sharp: He says his Democratic rival has made the U.S. less safe by failing to lead on the world stage.

Romney has roughed up Obama with a hawkish tone — at times bordering on belligerent. Yet for all his criticisms of the president, it has been difficult to tell exactly what Romney would do differently.

He has argued that reelecting Obama will result in Iran having a nuclear weapon — without explaining how. He has charged that Obama should have taken "more assertive steps" to force out the repressive regime of Syrian President Bashar Assad — but has said he is not "anxious to employ military action." He accused Obama of tipping his hand to the Taliban by announcing a timeline for withdrawal of American troops from Afghanistan, but also accepts the 2014 timeline.

Romney's approach could be seen in his take on the case of Chen Guangcheng, the blind Chinese activist who in early May sought shelter at the American Embassy before leaving his country. As Americans officials negotiated over his fate, Romney suggested that the Obama administration had put Chen in danger to placate the Chinese.

He said that if reports he had heard were true, "this is a dark day for freedom and it's a day of shame for the Obama administration."

Two weeks later, when Chen arrived in New York, Romney declared himself "relieved" and said the episode "underscores the need for the United States to forthrightly stand up for the human rights of the Chinese people."

At no point did he elaborate on how his approach would have differed from Obama's.

Christopher Preble, a foreign policy expert at the Cato Institute, a libertarian think tank, says he does not yet see "a huge difference" between the foreign policy approaches of Obama and Romney.

"A lot is made of Romney's tough talk with respect to Russia and Iran and China, but even there it's not like I see a dearth of toughness on the part of President Obama," Preble said. "As a challenger, for someone like Mitt Romney, it really is incumbent on him to draw distinctions and differences. He doesn't. It allows people to paint with a broad brush [what] they would guess … his response would be."

By portraying his opponent as a feckless commander in chief, Romney is playing on historic Republican criticisms of Democrats as insufficiently tough. But that task is more difficult this year as he faces a war-weary public and an incumbent president with some notable foreign policy victories, including the targeted killing of Osama bin Laden.

Foreign policy is not Romney's strength; 2008 GOP nominee John McCain defeated the former Massachusetts governor in primaries that year in part because of his international expertise. In Washington Post-ABC News poll last month, 53% of respondents said they trusted Obama to do a better job handling international affairs. Thirty-six percent picked Romney.

That may also be due to the lack of distinctions between the two. In 2008, Obama and McCain used the wars in Iraq and Afghanistan to differentiate themselves from primary opponents, and their proposals remained a central issue until the economic collapse that September.

This year, Romney and Obama agree on the basic timeline of the troop withdrawal from Afghanistan; Romney's chief critique has been his assertion that the president's actions are driven by political considerations. He says he would give greater deference to the generals on the ground.

Romney did not agree with Obama's decision to withdraw 33,000 surge troops before the end of the fighting season this year. But neither candidate has offered specifics on what size the U.S. combat force should be in 2013.

On Iran, Romney frequently faults Obama for waiting too long to put "crippling sanctions" in place on the central bank and the petroleum industry, measures that the Obama administration agreed to late last year. But when asked what further steps Romney would take to crack down on Iran, campaign aides said they were keeping an eye on legislation working its way through Congress that would put sanctions on regime officials and that Romney's main task would be to make sure the current sanctions are vigorously enforced.

In addition, Romney has said he would do more to support dissidents in Iran and make it clear that military action by the U.S. is a real option (something Romney charges Obama has failed to do, though the president has repeatedly said all options are on the table).

Two areas where clear differences exist are on policy toward Syria and on defense spending. On Sunday, Romney reiterated his call for the U.S. to work with Turkey and Saudi Arabia "to organize and arm Syrian opposition groups" with the goal of forcing Syria's Assad from power.